A subcutaneous mass on the neck of a horse

A 25-year-old Arabian gelding was presented for investigation of a subcutaneous neck mass. Fine-needle aspirates and impression smears revealed mast cells with widely varying degrees of cytoplasmic granulation and scattered eosinophils. Histopathology revealed a poorly circumscribed mass composed of sheets and bundles of mast cells with a large population of eosinophils. The mast cells were separated into numerous lobules by a heavy collagenous stroma, and multifocal collagen necrosis was present. Strong reactivity of the tumor cells for both Giemsa and toluidine blue stains confirmed the diagnosis of a mast cell tumor, and a Luna stain accentuated the eosinophilic infiltrates. Cutaneous mast cell tumors are found in many domestic animals but are uncommonly encountered in horses. Equine cutaneous mast cell tumors are usually benign, and there are no reports of visceral metastasis. Surgical excision is thought to be curative.     

Comparison of four staining methods for detection of mast cells in equine bronchoalveolar lavage fluid

Mast cells normally are present in equine bronchoalveolar lavage fluid (BALF), but usually represent <2% of all cells in healthy horses. An increased percentage of mast cells has been associated with airway hyperactivity and inflammatory airway diseases, but marked differences are reported between studies in normal and diseased horses. Because an abnormal mast cell count may be of clinical relevance, we compared the ability of a fast Romanowsky method to stain mast cell granules with that of 3 metachromatic stains: automated Romanowsky, May-Grünwald Giemsa, and toluidine blue stains. The BALF cells from 24 horses were studied. A differential cell count was performed blindly on 400 cells. The percentages of mast cells obtained were analyzed by means of repeated-measures analysis of variance and Fischer's PLSD test. The Bland and Altman method was used to assess agreement among stains. The mean percentage of mast cells in BALF was significantly lower with the fast Romanowsky than with the automated Romanowsky, May-Grünwald Giemsa, and toluidine blue stains. With the fast Romanowsky stain, the metachromatic granules of mast cells were not stained, and their identification was based on morphologic criteria. Toluidine blue staining allowed detection of the highest mean percentage of mast cells, but was inadequate for performing a differential cell count on other cell types. In conclusion, fast Romanosky stain may be inadequate for detection of mast cells in equine BALF, whereas automated Romanowsky, May-Grünwald Giemsa, and toluidine blue stains provide metachromatic staining of mast cell granules.     

Unilateral intraocular mastocytosis and anterior uveitis in a dog with subcutaneous mast cell tumors

A 9‐year‐old male castrated Scottish terrier was referred to the Radiation Oncology Service at the William R. Pritchard Veterinary Medical Teaching Hospital for palliative radiation therapy of an incompletely excised, recurrent subcutaneous mast cell tumor (MCT) located over the right scapula, and surgical removal of a perianal MCT. Three weeks after initial presentation and prior to the fifth radiation treatment, the patient was presented with cloudiness of the left eye of 3–7 days duration. Ophthalmic consultation revealed 3+ aqueous flare with a dependent, swirling component filling approximately one‐third of the anterior chamber. Aqueocentesis was performed under general anesthesia. Cytology revealed mast cells with highly atypical morphology and considered most consistent with neoplasia. The patient died 7 months after pathologic diagnosis of MCT on the right shoulder and 2 months after the cytologic diagnosis of malignant mast cells in the left anterior chamber. To the authors' knowledge, this is the first report of intraocular involvement in a mammal with MCTs, described here as intraocular mastocytosis.     

Granulosa thecal cell tumour in a mare causing hypertrophic osteopathy

Hypertrophic osteopathy (HO) is a rare condition in the horse characterised by symmetrical proliferation of connective tissue and subperiosteal bone, along the diaphyses of limb bones. In this case, a 10‐year‐old Irish Draught cross Thoroughbred mare was presented for investigation of weight loss, lethargy and firm swelling of all 4 distal limbs. Radiographs of the distal limbs revealed palisade‐like periosteal new bone formation perpendicular to the cortex of the distal third metacarpal and metatarsal bones, proximal (P1) and mid (P2) phalanges. Rectal examination revealed a mass of approximately 20 x 30 cm in the right caudoventral abdomen. The mare was diagnosed with HO due to a granulosa thecal cell (GTC) tumour. The GTC tumour was removed and the diagnosis confirmed on histological examination. Clinical examination and radiographs of the distal limbs after surgery demonstrated reduction in size of the limb swellings and new bone formation. To the authors' knowledge this is the first report of HO due to a GTC tumour in a mare.     

Zinc-responsive dermatosis in a red wolf (canis rufus).

An 18-mo-old male red wolf (Canis rufus) presented with footpad hyperkeratosis, suppurative paronychia, distal limb pyoderma, and peripheral lymphadenopathy. Diet for the previous 11 mo consisted of a mixture of two commercially prepared dog foods with a mineral supplement containing primarily calcium. Culture of the draining tracts on the distal limbs yielded a mixed population of opportunistic bacteria. Histopathologic findings were consistent with a diagnosis of zinc deficiency. Medical therapy consisted of 15 mg/kg amoxicillin p.o. b.i.d. and 10 mg/kg zinc sulfate p.o. s.i.d. Calcium supplementation was discontinued. Clinical signs resolved by 10 wk after the initiation of treatment.     

Multinodular Malignant Cutaneous Mast Cell Tumor in a Horse With Generalized Pruritus and Reactive Fibrosis: A Case Report

Mast cell tumor (MCT) has long been considered as an uncommon neoplasm in horses. Cytological and behavioral evidence of its malignancy is usually lacking, and only a few reports have described MCT displaying malignant behavior. An 18-year-old Friesian stallion presented with a one-year history of intermittent and progressive skin lesions on the left forelimb associated with intense, generalized pruritus and apathy temporarily responsive to glucocorticoids and antibiotics. The horse was alert and responsive with poor body condition and marked generalized pruritus. The left forelimb was markedly enlarged and surrounded by numerous firm 2- to 20-cm masses that were ulcerated and focally necrotic. A 7-cm round firm mass was observed on the left dorsal neck. Dermatological examination revealed generalized moth-eaten alopecia and scaling with erosions and ulcers secondary to pruritus. A direct skin smear from the affected leg showed severe eosinophilic inflammation and neutrophilic inflammation with pleomorphic bacteria. Histopathology of the skin and biopsies of the underlying tissues revealed an abundant population of atypical mast cells consistent with a malignant MCT. The horse was euthanized and necropsy revealed a marked fibrous reaction on longitudinal sections of the affected limb, and the tumor could be detected on only a few histological slides. Diagnosis of equine MCT can be challenging because of the massive accompanying fibrous reaction. Mast cell tumor should be suspected in the presence of eosinophilic infiltration of the affected tissue and in cases of generalized pruritus not attributable to other causes.     

IMAGING DIAGNOSIS—EQUINE MAST CELL TUMOR

Equine mast cell tumors are typically benign solitary growths of the head, neck, trunk, or limbs. When involving the limbs, these masses tend to be adjacent to joints without involving them. In radiographs there is often a well-circumscribed soft tissue mass with granular mineralization. The Arabian breed appears to be over represented. Surgical removal is usually curative. In this report, we describe the diagnosis, clinical features, and management of mast cell tumors in the rear limb of a horse.     

Grey eosinophils in a Miniature Schnauzer with a poorly differentiated mast cell tumor

A 10‐year‐old female spayed Miniature Schnauzer was presented for investigation of an intra‐nasal mass. The mass was diagnosed by histopathologic examination as an undifferentiated round cell neoplasm with an infiltrate of segmented leukocytes, interpreted as neutrophilic inflammation. The mass was treated with palliative radiation and systemic chemotherapy due to the presence of regional lymph node metastasis. During subsequent monitoring over several months, the peripheral leukocyte concentration was repeatedly within reference intervals to slightly increased with low numbers of toxic neutrophils. Four months after the initial diagnosis, there was a significant leukocytosis of 66 100 cells/μL, and 39 700 cells/μL of the leukocytes had variably mature, lobulated, and hypolobulated nuclei, and grey cytoplasm with clear vacuoles, resembling grey eosinophils. To further characterize these cells, peripheral blood smears from the patient and a canine control with eosinophilia were stained for alkaline phosphatase (AP), peroxidase, and esterase activities, and with Luxol fast blue (LFB). Histopathologic sections of the nasal mass were stained with LFB and immunohistochemically for tryptase. On blood smears, the cytoplasm of the suspected grey eosinophils stained for AP and granules stained with LFB confirmed that there was an eosinophilic lineage. Peroxidase staining was weak, and esterase staining was absent. On histopathologic sections from the nasal mass, the segmented leukocytes contained LFB‐staining granules, indicating an eosinophilic infiltrate was present. Neoplastic cells expressed tryptase, which confirms a mast cell lineage. Our findings suggest that grey eosinophils might be under‐recognized and interpreted incorrectly as toxic neutrophils. This report expands the canine breeds in which these eosinophils have been identified.     

Malignant mast cell neoplasia with local metastasis in a horse

A 12-year-old Arab stallion was presented with a chronically swollen right carpus resulting in profound lameness of the same leg. An incisional biopsy of subcutaneous tissue from the right carpus submitted for cytology and histopathology revealed large numbers of eosinophils interspersed by substantial numbers of variably sized and granulated mast cells. Fungal culture of a subcutaneous tissue sample taken from the right carpus was negative. Serial full blood counts revealed persistent mature eosinophilia, not accompanied by a mastocytaemia, neutrophilia without left shift and persistent hyperfibrinogenaemia. After humane destruction, dissection of the affected limb revealed a thick layer of connective tissue deposited around the right carpal joint. Within the connective tissue were embedded many small 0.25-1 cm diameter yellow gritty nodules, which consisted of dystrophic calcification and necrotic cell debris. The tendons enveloped by the connective tissue mass had limited function. The right axillary lymph node was moderately enlarged, yellow-brown and moist. Histopathological examination revealed a moderately well differentiated mast cell neoplasm with evidence of metastasis to the regional lymph node. In horses, malignant mast cell neoplasia is rare, while metastasis has only been reported in one other horse. Eosinophilia associated with equine mast cell neoplasia has not been reported previously but is recorded in mast cell neoplasia in the dog.     

Comparison of tracheal aspirates and bronchoalveolar lavage in racehorses. 1. Evaluation of cytological stains and the percentage of mast cells and eosinophils

OBJECTIVE: To compare a fast Romanowsky cytological stain (Diff-Quik) and Leishman's stain for the detection of mast cells in samples from the lower airways of racehorses, and to compare the proportion of mast cells and eosinophils in the total inflammatory cells in tracheal aspirate (TA) with those in paired bronchoalveolar lavage (BAL) samples. DESIGN: Retrospective case series of 48 young Thoroughbred and Standardbred racehorses. PROCEDURE: Fifty-one paired TA and BAL samples were collected after treadmill exercise from 48 horses with poor racing performance. Two slides were prepared from each sample; one was stained with Diff-Quik stain and the other with Leishman's stain. Differential cell counts of eosinophils and mast cells were recorded from each slide. Comparison of the suitability of the stains for the detection of mast cells, and comparisons of eosinophil and mast cell percentages in TA and BAL samples were analysed using the non-parametric Wilcoxon matched pairs test. RESULTS: Percentages of mast cells were significantly higher in Leishman than in Diff-Quik stained slides in both TA (P = 0.03) and BAL samples (P < 0.0001). Mast cell percentages were significantly higher in BAL than in TA samples using Leishman's stain (P < 0.0001). There was no significant difference in eosinophil percentages between TA and BAL samples (P = 0.07). CONCLUSIONS: Fast Romanowsky type stains (for example Diff-Quik) are not appropriate for the detection of mast cells in samples from the equine lower respiratory tract. Therefore, a metachromatic stain that reliably identifies mast cells (for example Leishman's) should be used if evaluation of mast cells in lower respiratory tract is undertaken. Mast cells are predominantly found in the distal small airways and alveoli sampled with a BAL. In contrast, eosinophils appear to be evenly distributed in the lower respiratory tract. However, high percentages of eosinophils are occasionally found only in TA samples. We recommend that both a TA and BAL be used for the evaluation of eosinophils and mast cells within the equine lower respiratory tract.     

The distribution and heterogeneity of mast cells in tongue from five different avian species

This study was conducted with the aim of determining the morphology, distribution and heterogeneity of mast cells in the tongues of seagull (Larus fuscus), common buzzard (Buteo buteo), goose (Anser anser), white stork (Ciconia ciconia) and Gerze rooster. The study used five samples of tongue material from each of the healthy adult avian species. The samples were fixed in 10% neutral‐buffered formalin (NBF) solution, then, after routine tissue follow‐up, the samples blocked with paraplast. Cross‐sections with 5–6 μm of thickness were stained with the 0.5% toluidine blue and alcian blue/safranin O (AB/SO). In all five avian species, it was found that the mast cells were in different sizes and round, oval or spindle‐shaped based on their place of distribution. Mast cell numbers were determined in stained with toluidine blue, examined ×40 objectives in a 1 mm² area. It was observed that mast cell density in subepithelial lamina propria and microscopic papilla was higher in the tongues of all species. Mast cell distribution and heterogeneity varied through the tongue, and there were more mast cells in the dorsal side of the tongue than the ventral side. The highest amount of mast cells was found in the tongue of the Gerze rooster among all five species. In the tongue cross‐sections stained with the combined method of alcian blue/safranin O (AB/SO), the mast cells were stained as AB (+), SO (+) and AB/SO (+) (mixed).     

Immunoglobulin E-bearing cells and mast cells in skin biopsies of horses with urticaria

The pathogenesis of equine urticaria is not well understood. In man, urticaria has been associated with immunological and nonimmunological mechanisms leading to the release of various mediators by mast cells. Skin biopsies of 32 horses with a history of urticaria were stained with toluidine blue, a double-labelling method for chymase and tryptase, and immunohistochemistry for immunoglobulin (Ig)E. These horses were compared with horses with pemphigus foliaceus, insect bite hypersensitivity and control horses with healthy skin. Neither formalin fixation time nor biopsy site influenced the staining methods. No chymase-positive cells were found. In all groups of horses, cells staining with toluidine blue and for tryptase and IgE were found in the epidermis and hair follicle papilla and significantly more positively staining cells were observed in the subepidermal dermis compared with the deep dermis. Horses with urticaria had significantly more IgE-bearing cells in the subepidermal dermis than control horses. However, horses with urticaria had significantly fewer toluidine-blue-stained mast cells in both subepidermal and deep dermis compared with the insect bite hypersensitivity and pemphigus foliaceus groups. This study suggests that IgE-mediated reactions play a role in the pathogenesis of urticaria.     

Amylopectinosis in fetal and neonatal Quarter Horses

Three Quarter Horses, a stillborn filly (horse No. 1), a female fetus aborted at approximately 6 months of gestation (horse No. 2), and a 1-month-old colt that had been weak at birth (horse No. 3), had myopathy characterized histologically by large spherical or ovoid inclusions in skeletal and cardiac myofibers. Smaller inclusions were also found in brain and spinal cord and in some cells of all other tissues examined. These inclusions were basophilic, red-purple after staining with periodic acid-Schiff (both before and after digestion with diastase), and moderately dark blue after staining with toluidine blue. The inclusions did not react when stained with Congo red. Staining with iodine ranged from pale blue to black. Their ultrastructural appearance varied from amorphous to somewhat filamentous. On the basis of staining characteristics and diastase resistance, we concluded that these inclusions contained amylopectin. A distinctly different kind of inclusion material was also present in skeletal muscle and tongue of horse Nos. 1 and 3. These inclusions were crystalline with a sharply defined ultrastructural periodicity. The crystals were eosinophilic and very dark blue when stained with toluidine blue but did not stain with iodine. Crystals sometimes occurred freely within the myofibers but more often were encased by deposits of amylopectin. This combination of histologic and ultrastructural features characterizes a previously unreported storage disease in fetal and neonatal Quarter Horses, with findings similar to those of glycogen storage disease type IV. We speculate that a severe inherited loss of glycogen brancher enzyme activity may be responsible for these findings. The relation of amylopectinosis to the death of the foals is unknown.     

Systemic mastocytosis with subcutaneous hemorrhage and edema in a Greyhound dog: case report and review of diagnostic criteria

Systemic mastocytosis, characterized by infiltration of multiple organs by neoplastic mast cells, is a well-described entity in human medicine with specific criteria for diagnosis, but is ill defined in veterinary literature. Hemostatic disorders are reported in humans affected by systemic mastocytosis but have not been well described in veterinary literature. A 5-y-old, spayed female Greyhound dog had a 1-mo history of progressive ventral cutaneous edema, hemorrhage, and pain. Cytology of an antemortem aspirate from the subcutis of the ventral abdomen was suggestive of mast cell neoplasia, but no discrete mass was present. The dog was euthanized and submitted for autopsy; marked subcutaneous edema and hemorrhage were confirmed. The ventral abdominal panniculus and dermis superficial to the panniculus carnosus were infiltrated by a dense sheet of neoplastic mast cells. The neoplastic cells contained toluidine blue–positive granules and formed aggregates within the bone marrow and several visceral organs, including the liver, spleen, heart, and kidney. Diffuse edema and hemorrhage is an unusual presentation of mast cell tumors in dogs. Antemortem tests, including complete blood count, coagulation profile, and viscoelastic coagulation testing, were suggestive of a primary hemostatic defect. We discuss here the diagnostic criteria used in humans, how these can be applied to veterinary patients, and the limitations of the current diagnostic framework.     

泌乳周期中外源物质对大鼠乳腺内肥大细胞数量的影响及乳腺组织内组胺含量的研究

选择泌乳期和静止期大鼠，经乳腺局部（乳导管）或外周（跖部皮下）注射辣根过氧化物酶（HRP）后，应用改良甲苯胺蓝染色法（MTB）对乳腺及其引流（鼠蹊部）和非引流（腘）淋巴结内的肥大细胞数量变化进行了研究，用荧光测定改良法检测了乳腺组织中组胺含量。结果显示，对照组乳腺及引流和非引流淋巴结内的肥大细胞数量均为静止期显著多于泌乳期（P〈0．01），乳腺中组胺含量也呈相同的变化趋势。在泌乳期从不同部位引人HRP后，乳腺及乳腺引流淋巴结内肥大细胞数量明显增多，与对照组相比差异极显著（P〈0．01）；而乳腺非引流淋巴结内肥大细胞数量则略有减少，与对照组相比差异不显著（P〉0．05）。在静止期从不同部位引人HRP后，乳腺及乳腺非引流淋巴结内肥大细胞数均减少，而乳腺引流淋巴结内的肥大细胞数则随引人部位不同而有差别：乳腺引人时增加，而外周引入时减少。本研究结果表明肥大细胞数量随生理周期的改变而增减的趋势与乳腺的发育、乳腺局部免疫状态及内分泌调节都有关系，而且不同泌乳阶段乳腺内肥大细胞对异物的易感性也存在差异。     

A case of pulmonary acariasis in lung of Japanese macaque

A 20-year-old female Japanese macaque, weighing 8.7 kg, developed severe pulmonary acariasis. Numerous whitish nodules, 2-4 mm, were scattered throughout the lungs. Histologically multifocal granulomatous lesions consisting of a large number of eosinophils, epithelioid cells, foreign body type giant cells, and collagen fibers were aggregated around the mait bodies. Numerous mast cells were also detected in the lesions by toluidine blue staining, and tested positive for tryptase by immunohistochemistry. This may be the first reported case of severe pulmonary acariasis in a Japanese macaque.     

二乙基己烯雌酚对成年仓鼠附睾肥大细胞数量分布的影响

成年雄性仓鼠经皮下连续注射二乙基己烯雌酚(DES)7 d后,用改良甲苯胺蓝染色法(MTB)和阿尔新蓝番红染色法(AB S)研究DES对附睾肥大细胞的形态大小、类型和数量分布的影响。结果表明:仓鼠附睾肥大细胞为结缔组织型肥大细胞,多分布于附睾头与附睾尾的被膜和间质中。试验组的肥大细胞常见于附睾管近旁,多呈脱颗粒状。虽然试验组与对照组的肥大细胞大小相近,但试验组的肥大细胞数量增多,尤其是附睾尾间质中肥大细胞增加明显(P<0.01)。     

Mastocytoma in the common carpal sheath of the digital flexor tendons of a horse

A 13-year-old Morgan gelding was examined for right forelimb lameness and tenosynovitis of the right common carpal sheath of the digital flexor tendons. The horse had moderate right forelimb lameness at the trot and marked effusion of the right common carpal sheath of the digital flexor tendons. Ultrasonographic examination revealed a soft tissue mass within the proximal pouch of the affected tendon sheath, located adjacent to the distal physis of the radius. Cytology and culture of the fluid revealed a sterile, eosinophilic tenosynovitis. Tenoscopic exploration confirmed the presence of a capsulated soft tissue mass. Thecotomy was required to fully debride the mass, which histology revealed to be a mast cell tumour. At 22 months postoperatively, the horse developed mild right forelimb lameness and eosinophilic tenosynovitis because of recurrence of the mastocytoma. Mastocytosis is a possible differential diagnosis in any horse exhibiting lameness associated with tenosynovitis. Surgical excision combined with rest and postoperative intrasynovial and systemic corticosteroids may be palliative.     

Disseminated pythiosis in three horses

Three cases of equine subcutaneous pythiosis with dissemination to the internal organs were investigated. The subcutaneous lesions were observed on the mammary gland, nostrils and limbs of the infected horses. Histopathological analysis of the infected tissues revealed a strong eosinophilic reaction, with macrophages, mast cells and giant cells. Sparsely septated hyphal filaments of 4-6 microm diameter were identified in the center of the eosinophilic areas. Specific fluorescent antibody against Pythium insidiosum confirmed the hyphae in the infected tissues in three examined horses. In one of the three cases, the DNA sequences amplified from the infected subcutaneous tissues and internal organs, revealed that P. insidiosum's 18S SSU rDNA amplicons shared 100% identity with those sequences deposit in GenBank. This is the first report confirming by immunochemical and genetic techniques that P. insidiosum can disseminated from superficial to deep structures.